1. Field of the Invention
This invention relates generally to sensors whose sensitivity is set via a potentiometer located within the sensor casing and which is encased in a potting compound.
2. Description of the Prior Art
In the assembly of a typical proximity sensor, the operate point, or sensitivity, of the sensor is set before assembly is completed. This is done because in a typical sensor, such as a proximity sensor, the sensitivity is set manually through direct contact with the potentiometer adjustment screw. The potentiometer and associated electronics, usually contained on a PC board, are then fitted within the casing of the sensor and surrounded with a setting, or potting, compound in a liquid state which then hardens to protect the components from outside environmental influences such as shock, moisture, or the like. However, upon this potting operation, the sensitivity or operate point, of the sensor may shift from the initial set point. If the sensitivity shifts far enough so that the sensor is no longer within specifications the sensor must be scrapped. Also, because of this limitation the design and layout of the components may need to be tailored around setting the sensitivity in the middle of the assembly process. Therefore, the assembly process may require methods such as multiple fillings and automated assembly interruption for manual intervention during assembly. These steps result in more time and expense to assemble the sensor.
Therefore, it would be desirable to have a method of constructing a sensor such that the potentiometer may be potted and then set to yield the proper sensitivity for the sensor thereby yielding a smoother assembly process and less out of tolerance sensors which must be scrapped. It would further be desirable to render the set point to the potentiometer, and thus the sensor sensitivity, stable against all outside influences once the sensor is completely constructed within specifications.
In order to accomplish the above purposes it is desirable to replace a potentiometer of the direct-contact, manually adjustable type with a remotely adjustable potentiometer, whereby the adjustment means may affect the set point of the potentiometer and thus the sensitivity of the sensor, after the sensor is completely constructed with its electronic components sealed within the case, such as by overmolding, sealing in a potting compound, or encased in a snap-together casing which is not easily separated.
This may be accomplished by substitution of a manually adjustable potentiometer with a digital potentiometer having remote adjustment means. However, because digital potentiometers may be knocked out of adjustment by having their set point affected by environmental transients, the remote adjustment line, once the proper set point has been obtained, is destroyed so that the sensor remains within specified operating parameters.